The problem with BMP files
BMP, short for bitmap, is one of the oldest image formats. It stores every pixel uncompressed, which makes the files enormous. A single photo saved as BMP can easily be ten or twenty times larger than the same image as a JPG. Those huge files are awkward to email, slow to upload, and wasteful of storage.
BMP is also poorly supported outside of legacy Windows software. Many websites, chat apps, and mobile devices will not display a BMP at all, and some outright reject the extension. This makes BMP a poor choice for sharing images with anyone.
Converting to JPG fixes both problems at once. JPG applies efficient compression tuned for photographs, cutting the file size dramatically, and it is accepted by virtually every application and platform in existence.
How the conversion works
This tool decodes your BMP with the browser and paints it onto an HTML canvas, then encodes the canvas as a JPG. Since BMP has no transparency, there is nothing to flatten, and the full image is preserved. Everything happens on your own device using the Canvas API, so no upload is required.
JPG uses lossy compression, so a small amount of detail is discarded to achieve the large size reduction. At standard quality this is not noticeable for typical photos and screenshots, while the file becomes a fraction of the original BMP size.
The converter is free, adds no watermark, and needs no account. It runs the same on desktops, tablets, and phones, so you can slim down a BMP wherever you are.